This invention relates to heat shields for roller tables, for example for use with transfer tables for supplying the finish roll stands of metal hot rolling mills.
This application is a 35 USC 371 of PCT/GB00/00708 filed Feb. 29, 2000.
In the hot rolling of steel in slab form, when a transfer bar is driven by rollers along a transfer table upstream of the finishing mill, heat loss from the bar will be greater at the side edges than at the centre of the bar. It is known to use electrical induction heaters to compensate for the increased heat loss and edges, but such heaters are both costly to install and expensive to operate.
It is also known to deploy heat shield panels around the hot material path to reduce heat loss, and in particular such heat shields have been employed to reduce the head-to-tail temperature variation along the length of a transfer bar.
For the reduction of transverse temperature variations by the use of heat shields, it has been proposed to make the heat shield panels laterally displaceable (EP 048503) to leave a gap at the centre of the hot material path so that the heat radiation rate over the control region is allowed to increase to be closer to the radiation rate at the edges, but usually there is insufficient space to allow this method to be employed effectively. It has also been proposed to tilt the upper panels to each side of the centre line of the material path to form a V-arched profile, but again only a very limited effect can be achieved due to space limitations.
It has also been proposed to pivot the bottom panels below the hot material path away from the path. While this may have a greater influence on the temperature variation across the width of the bottom face of the transfer bar, that will only have the desired effect at the top face of the bar if the bar thickness is not too great. For thicknesses of 25 mm or more, there will be an increasingly greater divergence of temperature between the opposite faces of the bar if heat is allowed to radiate freely from one face only.
In the industry, however, there is trend to produce larger and heavier finished steel strip coils using existing mill layouts. This required heavier and thicker transfer bars and bar thicknesses of 40-45 mm are now common, while thicknesses of 55 mm are known. With these increased thicknesses, not only is it not possible to effect the temperature distribution through the thickness of the bar by controlling heat loss from one face, but also the potential lateral temperature variation from increased edge heat loss grows greater.
According to one aspect of the present invention, there is provided a heat shield arrangement for a roller table comprising respective upper and lower series of heat shield panels above and below a hot material path along the table, the lower series of panels comprising at least one panel that is displaceable to permit a greater radiation loss from a central region of the path than from laterally outer regions to each side of said central region, the upper series of panels comprising at least one central panel and at least two laterally outer panels on opposite sides of said central panel, said outer panels being suspended from a primary support structure and said central panel being suspended from an auxiliary support structure displaceable relative to the primary support structure to raise said central panel relative to the outer panels.
By these means a more uniform lateral temperature profile can be obtained even for thick transfer bars. It will be understood, however, that when rolling slab thicknesses which are small enough for which sufficient control of temperature distribution to be exercised by regulating the heat loss from one main face of the hot slab, such regulation can be exercised from the top face alone.
According to another, more general, aspect of the invention, therefore, there is provided a heat shield arrangement for a roller table comprising a series of heat shield panels extending over a hot material path along the table, the panels comprising at least two outer panels on laterally opposite sides of at least one central panel, said central panel being displaceable to a raised position relative to the outer panels to permit an increase of heat radiation from a central region of the hot material path.
In a preferred arrangement according to this aspect of the invention, in the or each group of laterally juxtaposed panels, the outer panels are mounted on a primary support structure and said at least one central panel is mounted on an auxiliary support structure displaceable relative to the primary support structure to raise said central panel relative the outer panels.
Preferably, the auxiliary support structure is mounted on the primary support structure. If the heat shield panels over the table are required to be lifted quickly clear of the table, eg. to avoid being damaged by a deformed transfer bar, a displacement mechanism for the primary support structure will then be able to lift all the panels together. In an alternative arrangement, however, the outer panels are lifted, when required, by a displacement mechanism acting through the auxiliary support structure.
In a heat shield arrangement according to the invention, and in which displaceable central heat shield panels are located both above and below the hot material path, preferably displacement control means are adapted to move the upper and lower panels simultaneously away from the path.